1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming apparatus, and in particular, to a configuration for moving a stapling apparatus to a position where a stapling process is to be carried out.
2. Description of the Related Art
In the prior art, image forming apparatuses such as copiers, printers, and facsimile machines sometimes include a sheet processing apparatus which sequentially receives sheets such as copy sheets on which images have been formed and which then selectively carries out a stapling process, a punching process, or the like on the sheets. When the image forming apparatus includes such a sheet processing apparatus, time and effort required for processes such as stapling and punching which are carried out on sheets with images formed thereon can be reduced.
For example, to carry out a stapling process, the sheet processing apparatus includes a processing tray on which sheets to be stapled are stacked, a stapling apparatus that staples a sheet bundle on the processing tray, and a housing tray onto which the sheet bundle stapled on the processing tray are discharged.
Some such sheet processing apparatuses can carry out what is called a multi-stapling process including an end stapling mode in which one of the opposite end corners of one side of the sheet bundle is selectively stapled and a two-position stapling mode in which one side of the sheet bundle is stapled at two positions (see Japanese Patent Application Laid-Open No. 2005-132635). In the sheet processing apparatus, in the end stapling mode, the stapling apparatus is moved to a stapling position at the selected end to staple the sheet bundle. Furthermore, in the two-position stapling mode, the stapling apparatus is moved along one side of the sheet bundle to a first stapling position to staple the sheet bundle and then moved to a second stapling position to staple the sheet bundle again. The first and second stapling positions in the two-position stapling mode are pre-specified according to the sheet size.
Here, in some cases, when a stapling process is carried out, the sheet bundle stacked on the processing tray is moved to a stapling position by conveying means before the stapling apparatus staples the sheet bundle. Some sheet processing apparatuses include, for example, a gripping apparatus that grips sheets, as conveying means for moving the sheet bundle to the stapling position. Thus, the gripping apparatus gripping one side of the sheet bundle is moved to move the sheet bundle to the stapling position (see Japanese Patent Application Laid-Open No. H02-089772). Compared to a scheme in which the sheet bundle being pressed by a pressing member is conveyed to the stapling position, the above-described grip conveying scheme undergoes less misalignment in the sheet bundle. Furthermore, a conveying scheme is known in which one side of the sheet bundle is gripped by a gripping apparatus and in which the gripping apparatus is moved to convey the sheet bundle to a housing tray (see Japanese Patent Application Laid-Open No. 2005-132609).
In a sheet processing apparatus using such a grip conveying scheme, in the two-position stapling mode, the gripping apparatus is located on one side of the sheet bundle to be stapled. Thus, the stapling apparatus is prevented from moving along this side of the sheet, thus preventing the sheet bundle from being stapled. That is, the conventional sheet processing apparatuses fail to staple the portion of the sheet bundle where the gripping apparatus is located.
Thus, an object of the present invention is to provide a sheet processing apparatus and an image forming apparatus in which even when the apparatus includes a gripping apparatus that grips one side of the sheet bundle to be stapled, the portion of the sheet bundle where the gripping apparatus is located can be stapled.